The best nature writing from the newspaper, magazine, blog and book authors of the Lone Star State . . .

Thursday, April 17, 2008

Chimney Swifts, Our Aerial Acrobats by Ro Wauer

Last week I lifted off the metal chimney top that I install each fall. This invited chimney swifts back into our chimney for another season. And just like every other year, within a few days we could detect these little birds again taking up summer residency. It is one more pleasure of enjoying birds in South Texas!

Chimney swifts, one of our neotropical migrants, are widespread summer residents in Texas as far west as the Pecos River; they are less common in far West Texas and the Lower Rio Grande Valley. But as numerous as they are in Texas, and as closely associated as they are with people, for some reason they remain one of our most misunderstood birds. Perhaps that is largely due to their use of the dark interior of chimneys and other chimney-like structures for roosting and nesting. Perhaps people who fear bats have the same fear of other species that retire to the “dark side.” But this is silliness. Chimney swifts are not only one of our most fascinating birds but also one of our most beneficial species.

Like swallows and bats, chimney swifts obtain their food and water in flight; their diet consists primarily of flying insects and spiders on silken threads, and they skim water surfaces to drink. Ninety-five percent of a chimney swift’s diet consists of small insects, notably a wide variety of flies, and also ants, wasps, and bees. Swifts are the most aerial of all our birds and rarely fly alone; they usually feed in flocks of a few to many individuals. This habit probably helps them discovered insect swarms more readily than when searching alone. During migration, chimney swift flocks may number in the hundreds. Chimney swifts have been described as “flying cigars” due to their streamline body shape. They spend the vast majority of waking time in the air – feeding at various elevations, depending upon where they find the most flying insects, including the edge of thunderstorms, and courting with “V-ing” displays (wings held overhead in a V pattern) and amazing aeronautical skill.

At fist glance, a swift may be misidentified as a swallow, due to its similar behavior of feeding on the wing. But swifts are not swallows at all. They are members of the same order of birds as hummingbirds, the Apodiformes, the name derived from the Greek for “without feet.” That is a misnomer, however, because they do have feet, and although a swift’s feet seem tiny and weak, they are strong enough for birds in flight to break small twigs off trees for nesting material. Like hummingbirds, swifts are able to enter a state of torpor, their body temperature dropping as much as fifty degrees Fahrenheit for several hours at night or even for days during extremely inclement weather.

Another chimney swift habit that is out of the ordinary for birds is their use of chimneys for nesting; they once nested only in dark tree trunks and similar natural cavities. They now build their half-saucer-like nests on the inside walls of chimneys, cementing tiny twigs together and to the walls with gelatinous saliva. A nest described by John Tveten in Houston contained 130 twigs about the thickness of a toothpick or matchstick, and “all laid parallel along the longer axis of the nest, forming a half-saucer about four inches across and two inches deep.”

Only one nesting pair uses any given chimney, although the same chimney may hold several additional birds. These other birds may be either helpers – immature individuals that help the adults with various activities – or an unrelated roosting flock that occupies another portion of the chimney. The two to four nestlings are unable to feed themselves until 28 to 30 days old, so they are fed by their parents, which come and go as required. At this stage in the chimney swift’s life, their comings and goings to feed the young produce odd and strange sounds that, unless one is aware of what is taking place in the chimney can be rather frightening. But our chimney swifts are very welcome to share our home. And they are missed once they depart in summer for their wintering grounds in South America.